We added support for Amazon, Facebook, and Google identity federation to AWS IAM earlier this year. This poweful and important feature gives you the ability to grant temporary security credentials to users managed outside of AWS.
In order to help you to learn more about how this feature works and to make it easier for you to test and debug your applications and websites that make use of it, we have launched the Web Identify Federation Playground:
You can use the playground to authenticate yourself to any of the identity providers listed above, see the requests and responses, obtain a set of temporary security credentials, and make calls to the Amazon S3 API using the credentials:
The AWS Security Blog just published a step-by-step walkthrough to show you how the playground can help you to learn more about IAM and identity federation.